The invention relates to a method for seal-tightly attaching a flexible tubing of elastomeric material, especially of flexible members for air springs, to a connecting part by means of a clamping ring, which is radially pressed by a clamping tool. The invention further relates to a clamping tool for carrying out the method.
It is known to use a radially pressed-together metal clamping ring for pressing the end of a flexible member to the roll-off piston or to the cover of an air spring. The radial pressing of the clamping ring takes place with a clamping tool which comprises individual clamping jaws arranged to have a circular form. When clamping the clamping ring, the individual clamping jaws are moved so far toward each other until the required clamping between the wall of the flexible member and the connecting part (roll-off piston or cover of the air spring) is achieved.
What is decisive for the quality of the attachment of the flexible member is the precise achievement of the necessary clamping between the wall of the flexible member and the clamping region. The clamping cannot be too little because, in this case, the friction force, which results from the clamping, between the wall of the flexible member and the connecting part and therefore the required holding force of the wall of the flexible member on the connecting part is reduced. Likewise, the clamping force may not be too great because then the wall of the flexible member as well as the connecting part can be damaged. Furthermore, a clamping force which is too high and a deformation of the connecting part resulting therefrom can likewise lead to a reduction of the holding force.
Basically, two methods are known for attaching a flexible member to a connecting part of an air spring. In the one method, the clamping jaws of the clamping tool are moved toward each other with the force controlled, that is, the clamping operation is stopped when the force, which is generated by the clamping tool, corresponds to a pregiven force. The disadvantage of this method is that force tolerances can result in the total system and the force, which is generated by the clamping tool, therefore is not in a clear relationship to the force which arises between the flexible member and the connecting part.
Thus, it is, for example, possible that increased friction within the clamping tool occurs because of the deterioration thereof. In this case, an increased part of the force, which is applied by the clamping tool, has to be used to overcome this friction. For the same pregiven total force which the clamping tool generates, the force becomes less which adjusts between the flexible member and the connecting part as a consequence of the pressing of the clamping ring.
It is likewise possible that, when carrying out the method, clamping rings of different hardness are used. Only a small force is required to deform a soft clamping ring, whereas a large force is required for deforming a hard clamping ring. If a pregiven total force is generated in both cases by the clamping tool, then this leads, in the first case, to the situation that the force between the flexible member and the connecting part is increased and, in contrast, this force is reduced in the second case. Finally, the connecting part itself can have different stiffnesses, which, for a pregiven total force of the clamping tool, likewise leads to the situation that different forces adjust between the flexible member and the connecting part.
In the other known method, the clamping jaws of the clamping tool are moved together in a displacement-controlled manner, that is, a clamping operation is ended as soon as the clamping jaws have passed through a pregiven path. This method has the disadvantage that dimension tolerances in the components lead to different forces between the flexible member and the connecting part. If, for example, a clamping ring is used whose cross section lies below the pregiven cross section because of manufacturing tolerances, then this leads to a reduction of the force between the flexible member and the connecting part. On the other hand, the use of a clamping ring whose cross section lies above the pregiven cross section, leads to an increased force between the flexible member and the connecting part.
In summary, it can be said that, with neither of the two above-mentioned methods, flexible members can be connected to the connecting parts of air springs in such a manner that a pregiven defined force adjusts between the flexible members and the connecting parts of the air spring, which is the same for all manufactured air springs.
The invention has as its task to provide a method with which the clamping ring, which is used for attaching a flexible member to a connecting part, can be radially clamped in such a manner that a defined pregiven force adjusts between the flexible member and the connecting part. The invention likewise has the task of providing a clamping tool for carrying out the method.
According to the invention, the task is solved starting from a method of the above-explained type with the following method steps:
a force-displacement characteristic line of the clamping tool is determined, which is recorded during the radial clamping of the clamping ring with the recording being started before the connecting part, the flexible member and the clamping ring lying one against the other without force and without play;
the loss force, which is necessary for overcoming the friction in the clamping tool, is determined from the force/displacement characteristic line;
the force, which exceeds the loss force, is so adjusted that it corresponds to a pregiven force between the flexible member and the connecting part.
The advantages, which are achieved with the invention, are especially seen in that a defined pregiven force between the flexible member and the connecting part can be adjusted independently of xe2x80x9cforce tolerancesxe2x80x9d in the system (for example, different friction within the clamping tool or different hardness of the individual used clamping rings) and independent of dimension tolerances of the individual used components (that is, of the flexible member, of the connecting part and of the clamping ring). For this reason, neither a force which is too high nor a force which is too low can develop between the flexible member and the connecting part so that the initially-explained disadvantages and the disadvantages associated therewith cannot occur. A further advantage of the method is that it is simple to carry out and therefore the costs of a component manufactured in accordance with the method are not increased.
According to a first embodiment of the invention, the loss force is determined in the region of the force/displacement characteristic line in that the clamping tool is moved together so far that the connecting part, the flexible member and the clamping ring lie in contact with each other free of force and free of play.
It has been shown that the force/displacement characteristic line, which arises during the clamping action of the clamping tool, is essentially a straight line before and behind the region wherein the connecting part, the flexible member and the clamping ring lie one atop the other free of force and free of play. The straight lines have different slopes. According to a further embodiment of FIG. 3 of the embodiment of FIG. 2, the loss force is determined at that point at which the lines intersect (see the description with respect to the FIGS. as to how this occurs in detail). The advantage of this further embodiment is that the loss force can be determined in a simple manner at one point.
According to a further embodiment of the invention, the loss force is determined as follows:
the straight line ahead of the region (in which the clamping tool is moved together so far that the connecting part, the flexible member and the clamping ring lie one atop the other free of force and free of play) is extended beyond this region as a straight line;
from the extended line, during the further closing of the clamping tool for each path which the clamping tool has passed through beyond the above-mentioned region, the loss force corresponding thereto is determined.
The advantage of this further embodiment is that the loss force is exactly determined anew at each point during the radial clamping of the clamping ring after the clamping ring has come into contact at the flexible member. Starting from this exactly determined loss force, the pregiven force between the flexible member and the connecting part is adjusted (see the description of the FIGS. for more).
According to a further embodiment of the invention, the force/displacement characteristic line, which forms the basis of the determination of the loss force, is recorded anew at time intervals. This further embodiment is based on the idea that specific parameters, for example, the friction within the clamping tool, do not change with each clamping operation but only very slowly over a longer time span. Accordingly, the loss force can be determined with adequate accuracy based on a force/displacement characteristic line which has been determined once, if, during the repeated execution of the method, always the same components are used, that is, the same connecting part, the same flexible member and the same clamping ring (this is always the case in the manufacture of one charge). It has been established that the method according to the invention can be carried out with adequate accuracy when the established force/displacement characteristic line on the basis of which the loss force is determined is recorded anew every 100 to 10,000 clamping operations. The advantage of the further embodiment is that the force/displacement characteristic line only has to be recorded once for many clamping operations.
According to the further embodiment of the invention, the force/displacement characteristic line is recorded each time during clamping of a clamping ring and this recorded force/displacement characteristic line, during the clamping of this clamping ring, forms the basis for determining the loss force. The advantage of this further embodiment is that it makes possible an execution of the method with the largest possible accuracy. If it happens that for a charge of used clamping rings, which should all have the same hardness, one clamping ring exhibits a hardness deviating therefrom, then the magnitude of the loss force is influenced thereby. However, this is determined based on the actually recorded force/displacement characteristic line during clamping of this clamping ring so that also in this case, the defined pregiven force between the flexible member and the connecting part can be exactly adjusted (in contrast thereto, such a deviation could not be detected with the previous embodiment).
According to a further embodiment of the invention, the recordation of the force/displacement characteristic line is started before the clamping tool comes into contact with the clamping ring. The advantage of this embodiment is that the entire force/displacement characteristic line is recorded, which the clamping tool runs through during clamping of a clamping ring. From the total force/displacement characteristic line, additional information can be obtained in addition to the loss force. Accordingly, it can be determined from the force/displacement characteristic line how high the friction force within the clamping tool is. If this friction force exceeds a specific value, then maintenance of the clamping tool can be undertaken. Furthermore, it can be determined from the entire force/displacement characteristic line, for example, when the clamping jaws of the clamping tool come in contact with the clamping ring for the use of a charge of clamping rings, which all should have the same cross section. If contact does not take place after the clamping tool has run through a specific displacement, then this is an indication that, because of inadvertence, a non-suitable clamping ring has been placed in the clamping tool (if the cross section of the clamping ring, for example, is significantly too large because an incorrect clamping ring was placed), then this leads to the situation that the clamping jaws of the clamping tool come into contact with the clamping ring significantly earlier than if a proper clamping ring had been placed.